Datasheet LTC1778, LTC1778-1 (Analog Devices)
| Manufacturer | Analog Devices |
| Description | Wide Operating Range, No RSENSE Step-Down Controller |
| Pages / Page | 24 / 1 — FEATURES. DESCRIPTIO. No Sense Resistor Required. True Current Mode … |
| Revision | B |
| File Format / Size | PDF / 273 Kb |
| Document Language | English |
FEATURES. DESCRIPTIO. No Sense Resistor Required. True Current Mode Control. Optimized for High Step-Down Ratios. tON(MIN). 100ns
Model Line for this Datasheet
Text Version of Document
LTC1778/LTC1778-1 Wide Operating Range, No R TM SENSE Step-Down Controller
U FEATURES DESCRIPTIO
■
No Sense Resistor Required
The LTC®1778 is a synchronous step-down switching ■
True Current Mode Control
regulator controller optimized for CPU power. The con- ■
Optimized for High Step-Down Ratios
troller uses a valley current control architecture to deliver ■
tON(MIN)
≤
100ns
very low duty cycles with excellent transient response ■
Extremely Fast Transient Response
without requiring a sense resistor. Operating frequency is ■
Stable with Ceramic COUT
selected by an external resistor and is compensated for ■ Dual N-Channel MOSFET Synchronous Drive variations in VIN. ■ Power Good Output Voltage Monitor (LTC1778) Discontinuous mode operation provides high efficiency ■ Adjustable On-Time (LTC1778-1) operation at light loads. A forced continuous control pin ■ Wide VIN Range: 4V to 36V reduces noise and RF interference, and can assist second- ■ ±1% 0.8V Voltage Reference ary winding regulation by disabling discontinuous opera- ■ Adjustable Current Limit tion when the main output is lightly loaded. ■ Adjustable Switching Frequency ■ Programmable Soft-Start Fault protection is provided by internal foldback current ■ Output Overvoltage Protection limiting, an output overvoltage comparator and optional ■ Optional Short-Circuit Shutdown Timer short-circuit shutdown timer. Soft-start capability for sup- ■ Micropower Shutdown: I ply sequencing is accomplished using an external timing Q < 30µA ■ Available in a 16-Pin Narrow SSOP Package capacitor. The regulator current limit level is user program-
U
mable. Wide supply range allows operation from 4V to 36V
APPLICATIO S
at the input and from 0.8V up to (0.9)VIN at the output. , LTC and LT are registered trademarks of Linear Technology Corporation. ■ Notebook and Palmtop Computers No RSENSE is a trademark of Linear Technology Corporation. ■ Distributed Power Systems All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 5481178, 6100678, 6580258, 5847554, 6304066
U TYPICAL APPLICATIO
RON
Efficiency vs Load Current
1.4MΩ ION C 100 SS V V IN OUT = 2.5V 0.1µF VIN V C 5V TO 28V IN = 5V IN M1 RUN/SS TG 10µF Si4884 L1 50V 90 CC 1.8µH SW ×3 VOUT 500pF C 2.5V B 0.22µF VIN = 25V ITH BOOST 10A + COUT D R B 180µF C LTC1778 80 CMDSH-3 4V 20k SGND INTVCC ×2 M2 D1 EFFICIENCY (%) BG Si4874 + B340A C 70 VCC 4.7µF R2 PGOOD PGND 30.1k V 60 FB 0.01 0.1 1 10 R1 14k LOAD CURRENT (A) 1778 F01b 1778 F01a
Figure 1. High Efficiency Step-Down Converter
1778fb 1
U FEATURES DESCRIPTIO
■
No Sense Resistor Required
The LTC®1778 is a synchronous step-down switching ■
True Current Mode Control
regulator controller optimized for CPU power. The con- ■
Optimized for High Step-Down Ratios
troller uses a valley current control architecture to deliver ■
tON(MIN)
≤
100ns
very low duty cycles with excellent transient response ■
Extremely Fast Transient Response
without requiring a sense resistor. Operating frequency is ■
Stable with Ceramic COUT
selected by an external resistor and is compensated for ■ Dual N-Channel MOSFET Synchronous Drive variations in VIN. ■ Power Good Output Voltage Monitor (LTC1778) Discontinuous mode operation provides high efficiency ■ Adjustable On-Time (LTC1778-1) operation at light loads. A forced continuous control pin ■ Wide VIN Range: 4V to 36V reduces noise and RF interference, and can assist second- ■ ±1% 0.8V Voltage Reference ary winding regulation by disabling discontinuous opera- ■ Adjustable Current Limit tion when the main output is lightly loaded. ■ Adjustable Switching Frequency ■ Programmable Soft-Start Fault protection is provided by internal foldback current ■ Output Overvoltage Protection limiting, an output overvoltage comparator and optional ■ Optional Short-Circuit Shutdown Timer short-circuit shutdown timer. Soft-start capability for sup- ■ Micropower Shutdown: I ply sequencing is accomplished using an external timing Q < 30µA ■ Available in a 16-Pin Narrow SSOP Package capacitor. The regulator current limit level is user program-
U
mable. Wide supply range allows operation from 4V to 36V
APPLICATIO S
at the input and from 0.8V up to (0.9)VIN at the output. , LTC and LT are registered trademarks of Linear Technology Corporation. ■ Notebook and Palmtop Computers No RSENSE is a trademark of Linear Technology Corporation. ■ Distributed Power Systems All other trademarks are the property of their respective owners. Protected by U.S. Patents, including 5481178, 6100678, 6580258, 5847554, 6304066
U TYPICAL APPLICATIO
RON
Efficiency vs Load Current
1.4MΩ ION C 100 SS V V IN OUT = 2.5V 0.1µF VIN V C 5V TO 28V IN = 5V IN M1 RUN/SS TG 10µF Si4884 L1 50V 90 CC 1.8µH SW ×3 VOUT 500pF C 2.5V B 0.22µF VIN = 25V ITH BOOST 10A + COUT D R B 180µF C LTC1778 80 CMDSH-3 4V 20k SGND INTVCC ×2 M2 D1 EFFICIENCY (%) BG Si4874 + B340A C 70 VCC 4.7µF R2 PGOOD PGND 30.1k V 60 FB 0.01 0.1 1 10 R1 14k LOAD CURRENT (A) 1778 F01b 1778 F01a
Figure 1. High Efficiency Step-Down Converter
1778fb 1
